Cellular immune responses are thought to play a major role in immunity to bacterial infections. Bacteroides gingivalis is a gram-negative anaerobic rod that has been isolated from periodontal abscesses, endodontic abscesses and various medical infections and is thought to be an important microorganism in the etiology of human periodontal disease. Since the interactions between host and periodontopathogen that result in abscess formation or resistance to infection are poorly understood, this study proposes to look at these interactions using B. gingivalis in a mouse model. Mice will be immunized with B. gingivalis, or with bacterial extracts obtained by affinity chromatography using monoclonal antibodies conjugated to Sepharose 4B. Following immunization, mice will be challenged intraperitoneally or subcutaneously with viable G. gingivalis. Lymphocyte subpopulations and serum obtained from mice resistant to abscess formation will be used for passive transfer experiments to determine the roles of T cells, T-cell subsets, B cells and immune serum in protection against B. gingivalis. Lymphocyte subpopulations will be obtained using immunofluorescent cell fractionation techniques on an Ortho Cytofluorograf model 50H. Antigen-specific T-cell lines and B-cell lines will be established from immunized mice so that immune responses to B. gingivalis can be tested using homogenous populations of lymphocytes. Both in vivo (passive transfer experiments) and in vitro (blastogenesis, antibody production and adjuvant activity) immune responses will be analysed and compared. Antigen-specific T-cell and B-cell lines will be established from periodontal patients and the in vitro immune reactivity of these cell lines to B. gingivalis will also be analysed.